dotted.case

Using dot (.) as a separator is probably the least common of all of these. A common place you'll see this is with domains.

www.google.com

Also when working with JSON objects.

message.author.name

Another place I've seen it used is as keys in feature toggles, which is quite smart as it resembles accessing a JSON object property.

if (features.get("api.users.showPassword")) { ... }